Ventricular Arrhythmia | Sudden Cardiac Death

What is ventricular tachycardia?

Ventricular tachycardia (VT) describes a fast rhythm originating in either of the two main pumping chambers of the heart (the ventricles). During VT the heart doesn’t beat as efficiently as normal and as a consequence symptoms including palpitations, breathlessness, chest pain and dizziness are often present. Rapid ventricular tachycardia may lead to loss of consciousness and degenerate into ventricular fibrillation, causing cardiac arrest (figure 1).

Common causes of VT include coronary disease and cardiomyopathy, but it may also occur in patients with a structurally normal heart. In these patients VT may be associated with a genetic condition such as long QT syndrome or Brugada syndrome.

Ventricular tachycardia and coronary disease

Narrowing or blockage of one or more coronary arteries may lead to replacement of heart muscle with scar tissue. VT can arise from areas around scars and increases the risk of sudden cardiac death. Cardiac investigations such as echocardiography (cadiac ultrasound) are useful to assess left ventricular function, and coronary angiography may be required to identify the severity of coronary artery disease. Some patients may also require revascularisation with coronary balloon angioplasty and stenting or coronary artery bypass surgery. An electrophysiological study (electrical study of the heart) may be required to assess the circuits responsible for VT. Treatment strategies include antiarrhythmic drug treatment, catheter ablation and, more commonly, implantable cardiac defibrillator (ICD) therapy (figure 2). In this setting an ICD provides the greatest protection against sudden cardiac death.

Ventricular tachycardia and cardiomyopathy

Cardiomyopathies, diseases of heart muscle, can result in VT and sudden cardiac death. The two main forms of heart muscle disease are hypertrophic and dilated cardiomyopathy, but arrhythmogenic right ventricular dysplasia, a disease predominantly of the right ventricle is being increasingly recognised as a cause of VT, and other signs of this condition may be absent in the early stages of the disease. Echocardiography is required to assess left ventricular function and heart cavity size, and coronary angiography may be required to identify the presence or absence of coronary disease. Most patients will require ICD therapy for protection against the risk of sudden cardiac death, but catheter ablation may be useful to target a focus or circuit causing recurrent VT.

Ventricular tachycardia and the structurally normal heart
VT can occur in the absence of coronary disease or cardiomyopathy. In these patients it is usually benign rather than life threatening but can be highly symptomatic. Investigations required include echocardiography and in some, coronary angiography. Catheter ablation is often successful in eliminating the focus or circuit responsible for the arrhythmia and effecting cure (figure 3).

Ventricular tachycardia and Long QT syndrome and Brugada syndrome
Long QT syndrome

Long QT syndrome is a genetic abnormality that can lead to VT and cardiac arrest. The diagnosis is usually made by a 12 lead ECG, but an exercise test may be required to identify those with latent long QT syndrome manifest as a lack of QT shortening during exercise. Beta-blockade remains the mainstay of treatment, especially in the type l and ll subtypes, but symptomatic patients despite beta-blockade may require defibrillator implantation or sympathectomy. Long QT type 3 patients are at particular risk as their first presentation may be sudden cardiac death, and prophylactic implantation of an ICD is recommended.

Brugada Syndrome

Patients and relatives with Brugada syndrome, an inherited condition similar to long QT syndrome, are at increased risk of ventricular arrhythmias and sudden death. Like long QT syndrome, electrocardiographic changes may not be present at rest and drug challenge with ajmaline or flecainide may be needed to reveal the underlying ECG abnormalities. Those with a history of blackouts or documented ventricular arrhythmias require an ICD for long term protection against the risk of sudden death. Asymptomatic patients require further risk stratification by means of an electrophysiological study, with those with inducible ventricular arrhythmias also requiring an ICD.